Phase-shifting network



June 18, 1929. NYQUIST JUAOB PHASE SHIFTING NETWORK Filed Aug. 25, 1926I ZZZ/02.6

IN I! EN TOR flW 0 BY I t A TTORNEY S.

same an. is, 1929. 1,117,400

UNITED STATES PATENT OFFICE.

HARRY NYQUIST. OF MILLBUEN, NEW JERSEY, ASSIGNOB. TO AMERICAN TELEPHONEAND TELEGRAPH COMPANY, A. CORPORATION 01 NEW YORK.

PEASE-SHIFTING NETWORK.

Application filed August 25, 1926. Serial No. 131,495.

This invention relates to a network by of this being determined by thecharacterwhich a source of alternating current voltage istics of thenetwork appearin between the 55 may be obtained, the phasethereof beingconin mt and output terminals. T iie network in veniently controlled andvaried. The netthlsfi ure comprises twobranches in parallel 5 workcomprises a circuit with two input each Eranch being made up of twohalves terminals to which an alternating current and each half comrising a reactance element source may be connected, and two output and aresistance e ement. More specifically 60 terminals from which potentialdifference the one branch is made up of the followin b bta'dtl 1 ft]tt'l e 0 me Xe pw'se 0 en la elements taken in order: An inductance 10di erence being completely controlla le with- 2 out altering thecondition of the source. The R R invention may find application in manya reslstence 5 a Second i ce 5 and an 65 places such as that illustratedin my applica- L tion Serial No. 90,653, filed February 25,1926,Inductance The second branch is similarlvlvsllch one form of myinvention is shown 1 made up of the following lments taken The par oseof this invention is to design a in the order of a capacity a resistance70 networ 0 these general characteristics, and, R 2

at the same time, one which Will provide a resistance :2. and a capacityIt will 2 source of alternating electromotive force,

appear later that the mldpoints O, and 0 which, while variable in phase,shall be constant in amplitude of the two branches are at the samepotential 75 Still a further purpose of the invention is and therefPrethere 13 oblectlon and i to provide such a source which shall be as somei It may be aJdwmtageous to connect simple as possible in itsadjustments to obthese filrectly b n h wn. For tain the desired phaseshift and as simple in mmphclty of g the reslsmflces e 11 itsadjustments as possible for changes in made oftbe q e mm s Varmble socontact wlth a point on the resistances in each 7 frequency. Theinvention will be better understood from the following descriptionbranch are two cflmductms 6 and 7 leading to the output terminals 3.

taken in connection with the accompanying drawings which embody certainexamples of In Order to Obtam i"? results deslleda the my invention theinvention it lf being inductances and capac ties are made of such 85value that for the particular frequency given fined by the appendedclaims.

In the drawing Figure 1 represents one the generator A there shall existthe rea ion form of network for obtaining the desired shift in phase ofan alternating current 1 source. Fig. 2 is a modification thereof. p"ifi' Figs. 3 and 4 are still further modifications in which one type ofreactance element only where g 20 and 5; represent the inductance 40 isused, Fig. 5 is a vector diagram of E. k

F.s involved in the circuits and Fig. 6 is a and capacity and resistanceof the various eleview of a mechanical device for o aining ments shown,and =21ra: frequency. The the desired phase shift. reason for thisrelatlonship will bebetter un' Referring more articularly to Fig 1,there (iOIStOOd by the fOllOWlDg COIlSldBIfltlOllS. 45 i shown source flt ti E, M F The current flowing through the capacity A. this sourcehaving any desired frequency branch W1 1 be which we may represent by f.This source e is connectedto the input terminals of a net 1 R 1 (2).work which has two output terminals 3, from which, by suitableadjustment, it will be possible to obtain an alternating current voltageWhere 6 IS the p tentgl difference across the of the frequenc given bythe generator A, network and j= /1 and where the de- 1 5 but ofcontrolla le phase and magnitude, all nominator of this expressionrepresents the which shows that the currents in the two branches are notin phase with each other. If we give the inductances and ca acities suchvalues that the relations 1) ho d, then these two current relations takeon the form e e (l 7') R(1 2R 9 and e e (1 7') R 1 j) T (5) from whichit appears that z', and a, differ in phase by 90.

The potential difference which exists between the point 0 and a point Sbetween which there exists the resistance 1', will then be O and a pointS the resistance 1' and that between the point between which thereexists will be The potential difference, then, between the points S andS as measured from output terminals 3 will be the difference betweenthese values, that is,

the magnitude e is given by 0b, which is 90 in phase behind orz. If thecontact 7 includes between itself and the point 0 an amount ofresistance 1' the potential difference over that resistance will be e,and is indicated as such in Fig. 5. Similarly, for a resistance 1' inop- I posite' branch there will be potential difference e,'. Theresultant of these two components, represented by their vector sum, isshown on the diagram as 00 and it will be noted that the magnitude andthe phase of his resultant will depend upon the values 1', and 1' It isalso evident that if the proper relationship is maintained between thesetwo resistances, that their vector sum will, in magnitude, always beequal to e, and such a relationship on the diagram is indicated by thetwo compliments e, and 6,. In order that this relations 'p shall bemaintained, it will be evident that the following shall hold where ugives the phase angle of the resultant, using the base of 0a as thereference. Under these conditions, it will be observed that while thephase of the resultant E. M. F. may be shifted through the angle 360 orany part thereof, the magnitude remains constant and this feature of aconstant magnitude with any desired change in the phase contitutes animportant feature of this invention. In order to accom lish this resultthe contacts S and S shouid be varied together in such manner as tomaintain the relationship given above and any suitable mechanism ma beused for this. One means for accomplis ing this is shown in Fig. 6, inwhich there are two crank-shafts 21 and 22 in parallel with each otherand each having two throws insulated from one another and 90 apart. Theconnecting rods 26 and 27 make contact respectively with and travel overthe resistances between the inductances of one branch and between thecapacities of the other branch of the network. In view of the circularmotion and the 90 phase relationship of the two arms, it is seen thatthe resistances included at any moment across the output terminals 3 ofFig. 1 are in accordance with the relations of Equation (9).

It is apparent that if the frequency of the generator A is changed,corresponding changes must be made in the inductances and in thecapacities or in the resistances in order to restore or maintain theconditions of relations (1). For this reason, it will be desirable tomake these variable or to make the resistances variable, and this isindicated in Fig. 1 by the arrows passing through the elements.

Various modifications may be made in the network in order to obtainsomewhat different results. In Fig. 2, for example, the number ofresistance elements of each branch have been increased and so locatedthat only half of the resistance of each branch occurs adjacent to thebridge 0 O The mathematical analysis in this case is similar to that forFig. 1, and differs only in that the maximum voltage at the outputterminals is onehalf as great.

In some cases, it may be desirable to reduce the number of types ofelements included in the network. This is particularly true if thefrequency of the generator A is to be changed in which case theadjustment which must be made may be brought about by changes in the'inductances or in the capacities. In general,

able inductances, and F 3 shows a circuit.

in which the inductances ve been dispensed with. As shown in thatfigure, the inductances of Fig. 2 have been removed, and the resistancesin that branch which are adjacent to the bridging point 0 are shunted bycondensers of capacity 20. In this case, it may be shown that thecurrent flowing through these resistances adjacent 0 1s given by and thecurrent through the branch which has not been altered is 121 1 1 y'pOR(11) If, now, the condition is set that similar to that of Fig. 1 anddescribed by means of Fig. 5 again exists. And if the same relationshipregarding the values of r,

and r, be maintained, then the output voltage will remain constant inamplitude without regard to the total change in phase.

In some cases, it may be desirable to use condenser units of the sametype or size in the two parallel branches. Such an arrangement is shownin Fig. 4, the capacities 20 being replaced by capacities 20 of the samesize as in the parallel branch. In order to maintain the properrelationships, it is necessary in this case to also alter the value ofthe resistances in the branch in which the condensers have been changed,these resistances now taking on the value In this case,

the current through the resistance r, is four times as great as that inr. but if the ad ustments are so controlled that sin b r cos b then theoutput voltage will be of constant magnitude and the same as that forFig. 3.

It may be mentioned that each of the circuits can be shown in a slightlydifferent form in which they take on the appearance of the conventionalVheatstone bridge network. Also it may be pointed out here that the iniput impedance of the network of Fig. 1 and of Fig. 2 is R, in both casesbeing pure resistances. On the other hand, the input impedances of Figs.3 and 4 can be shown to be equal, respectively, to

R R 3 -1) r- 2)- VVhat is claimed is:

1. A source of single phase alternating E. M. F. and a. networkassociated therewith adapted to serve as a source of E. M.VF. ofvariable phase, said network comprising two parallel branches across theterminals of said source, each possessing lumped reactance andresistance, and means for keeping the delivered E. M. F. of constantamplitude.

2. In a variable phase shift network, two branches in parallel, eachpossessing capaci tance and resistance, each branch as seen from itsmidpoint being made up of two identical portions with the elementsarranged in the same order, movable terminals attached to theresistances of said branches and adapted to deliver E. M. F. of variablephase and constant amplitude.

3. A variable phase shift network comprising two branches in parallel,each possessing reactance and resistance, each branch as seen from itsmidpoint being made up of two identical portions with the elementsarranged in the same order, terminals making movable contact with theresistances and means to so relate the movements of the contacts as todeliver E. M. F. of variable phase and constant amplitude.

4. In a variable phase shift network, two branches in parallel, eachpossessing capacities and resistances, each branch as seen from itsmidpoint being made up of two identical portions with the elementsarranged in the same order, and with resistance elements adjacent themidpoints, terminals making movable contact with the rcsistances, andmeans to so relate the movements of the contacts as to deliver E. M. F.of variable phase and constant amplitude.

5. A variable phase shift network for delivering E. M. F. of variablephase, comprising two branches in parallel adapted to be supplied froman AC source, the one branch comprising four equal resistance elementsin series and a condenser bridged across each of the two innerresistance elements, the second comprising four resistance elements inseries each equal to the resistance elements of the first branch andfurther comprising a condenser between each pair of outer resistanceelements, and variable contact leads from points on the inner resistanceelements.

6. A variable phase shift network for delivering E. M. F. of variablephase, comprising two branches in parallel adapted to be supplied froman AC source, the one branch comprising four equal resistance elementsin series and a condenser bridged across each of the two innerresistance elements, the second com rising four resistance elements inseries cac 1 equal to the resistance elements of the first branch andfurther comprising a series condenser adjacent each outer resistanceelement, and variable contact leads from points on the inner resistanceelements, the impedance of each of the shunting condensers in the firstbranch being one-half that of each of the resistance elements, and theimpedance of each of the condensers in the second branch being twicethat of each resistance element, the contact leads hein, so related intheir movement as to yield E. M. F. of constant amplitude.

7. In a variable hase shift network, two branches in paralle eachpossessing capacitance and resistance, each branch as seen from itsmidpoint being made up of two identical portions with the elementsarranged in the same order, movable terminals attached to theresistances of said branches, and means for so moving the terminals withrespect to each other that the potential difference across saidterminals shall be of constant amplitude and variable phase.-

In testimony whereof, I have signed my name to this specification this24th day of August, 1926.

HARRY NYQUIST.

